A hydro-electric project in the Severn Estuary worth more than £1bn could be the first in a series of collaborations between Cardiff and Bristol councils.

The two authorities plan to sign a memorandum of understanding once it has been approved by both cabinets.

If passed, Cardiff said the first joint initiative could be a twin tidal lagoon.

It follows plans for a £25bn barrage being described as "dead in the water" for the time being.

Utilising the Severn's tidal range - the second biggest in the world - it is claimed the lagoons could generate enough electricity to power the whole of the region.

As the biggest two authorities, Cardiff and Bristol had to take the initiative on this project and on the regional partnership as a wholeAshley Govier, Cardiff council's cabinet member for environment

"Obviously the tidal lagoon is what's catching the headlines today, but that's only part of something much bigger," said councillor Ashley Govier, Cardiff council's cabinet member for environment.

"Cardiff and Bristol are both too small to compete on our own with the city-regions of London, Birmingham and Manchester, but we can be big players if we work regionally and collaboratively.

"Taking charge of our own green and affordable energy needs is part of that, but also we need to work on housing, transport and a whole raft of issues to make the Severnside area a more attractive place to live and work."

The proposed system would see a network of hydro-turbines encased in a concrete wall at either side of the Severn Estuary.

The Severnside project is similar to one currently under consideration in Swansea.

However, while the Swansea lagoon would provide renewable electricity for 100,000 homes, the Cardiff/Bristol operation is projected to power double that - possibly more if neighbouring authorities came on board.

"As the biggest two authorities, Cardiff and Bristol had to take the initiative on this project and on the regional partnership as a whole," added Mr Govier.

"But we very much want to bring in our neighbouring authorities, so for us the Vale of Glamorgan, Newport etc and from Bristol's point of view the Somerset authorities."

The project would work by harnessing the Severn's tides behind concrete dams.

'Burdensome'

When there is a sufficient difference between the depths on either side of the dam, sluice gates would be opened to release the trapped water, turning turbines and generating the electricity.

Mr Govier said that while Cardiff and Bristol were in discussions with several private companies, he hoped it would remain a project which could ultimately benefit taxpayers.

"The scale of the tidal lagoon project we're envisaging would cost considerably more than £1bn, so it's obvious that the only way we could achieve it would be with private backing," he said.

"But it's not something we'd just sell on, it has to have a tangible benefit for the region and its people.

"We could either sell the electricity into the National Grid to raise income and reduce our reliance on taxation, or alternatively we could sell it to a specific electricity supplier with the caveat that it has to be passed on to consumers in the region at a heavily reduced rate."

He added: "As a council and a region we need to be doing more to make Severnside an attractive option for business to come to."

Hafren Power wants to build an 11-mile (18km) barrage between Lavernock Point near Penarth, Vale of Glamorgan, and Brean near Weston-super-Mare, Somerset.

But in September, barrage supporter and Neath MP Peter Hain said that plans for a £25bn barrage in the Severn Estuary were "dead in the water" in the current Parliament.

Mr Hain said the UK government had refused to commit to it.

In June, MPs said Hafren had failed to make the case that it would be good for the economy or the environment.